The present invention relates to a transfer material used in a printer, and more particularly to a transfer material for use in a type writer or a thermal printer and exhibiting an excellent dimensional stability and durability.
A polyester film has been used as the base of a transfer material used in a printer because of its high crystallizability, high melting point, and improved heat resistance, chemicals resistance, strength, and elasticity. The transfer material for use in a dot impact type printer needs to have durability of the level to withstand the tension or printing pressure applied to the transferring ribbon for the purpose of using it repeatedly. The transfer material for use in a thermal printer needs to have improved strength, heat resistance, and dimensional stability since the thickness of the base film thereof has been reduced recently.
However, the usual biaxially oriented polyester film of the type disclosed in Japanese Patent Laid-Open (KOKAI) No. 60-217194 for use as the base film encounters a problem of elongation of the film or plastic strain during the transferring operation. Therefore, the biaxially oriented polyester film has not been satisfactorily used as the transferring ribbon of the type to which high tension and high printing pressure is involved to be applied.
That is, when the strength of the film is strengthened in order to reduce the thickness of the film, the thus-strengthened film can be easily torn longitudinally. In a thermal printer, such a thin film cannot be used as a transfer material due to its excessive heat shrinking. Therefore, it has been difficult to reduce the thickness.
The inventor has studied in order to overcome the above-described problems and found that a transfer material in which a polyester film having a specific characteristic is employed can overcome the problems. The present invention has accomplished based on this finding.